Numerous methods of gene transfer are known in the art, and are not reviewed in any great detail here. Suffice it to say that in general, methods of gene transfer in vitro are well known and have been practiced for several decades. Methods of in vivo gene transfer are much more recent, but have been successfully applied in such contexts as gene therapy efforts to overcome genetic disorders, and in disease modeling efforts, such as the production of germ-line transgenic animal models, such as gene knockout mice or transgenic mice and other animals expressing heterologous genes.
In general, the known methods of in vivo gene transfer involve the knockout of single genes present in the genome of an animal model, or the inclusion in the germ-line of a specific transgene in the genome of an animal model. The limitations to such methods include the possibility of inducing terminal illnesses in the animal models, such that either non-viable fetuses are produced, or limited life-span animals are produced. In addition, the effects of multiple gene knockouts or transgenes are extremely difficult to simulate in such systems, due to the complex temporal, gene regulatory and interaction effects in such systems. Furthermore, the germ-line transgenic models currently available tend to provide data on a very slow time scale, and such efforts as drug modeling and disease analysis are delayed by the time-scale of transgenic animal maturation. Accordingly, there remains a need in the art for techniques which address and overcome these limitations. This invention is directed to resolving many, if not all, of these limitations in the art.